Gear tooth machining is a relatively expensive process in the field of gear unit production. This applies already to soft state machining, but in particular to machining after hardening, i.e. to precision hard finish machining. High capacity and high precision machines are required which, according to the high targeted ultimate accuracy of the gear teeth, must clamp the work pieces precisely, align the premachined tooth spaces accurately relative to the machining tool, and finally produce the desired geometry. Machining methods known today are chiefly grinding, but also hard milling, honing, skive hobbing, hard skiving and other processes.
Due to the expensive operation of tooth machining, but in particular hard finish machining, it is of the greatest interest to trim the machines for the highest possible productivity, and simultaneously to reduce idle times as far as possible. In recent years it has been possible to improve the machining processes such that they have become several times more productive. At the same time the feeding of the machines with work pieces has to a large extent progressed from the previously usual hand loading to automatic loading. Nowadays with the masses of gears being produced, the pure machining times often exceed the idle times by a negligible amount only—this not least due to the very unfavorable conditions for work piece handling, since the oils used in the process for cooling and lubrication, and the fine swarf produced by the machining operation are detrimental to a trouble free and exact loading of the machine. From this aspect it is obvious that a reduction of idle times and a lessening of the side effects of the process cooling/lubrication can contribute greatly to a further increase in efficiency.
Devices for a quick work piece change have long been known. On a hobbing machine, for example, by means of a ring loader fitted with two work piece grippers and swivel located on the machine body, a work piece blank and a finished work piece are grasped simultaneously and exchanged one for the other. The work piece blank is swiveled from a loading transfer platform outside the machine to the clamping device on the work spindle in the working area, and placed onto the said spindle, whilst at the same time the finished component is drawn off the clamping device and swiveled to the transfer platform. The disadvantage of this method is that the loading elements are totally exposed to the coolant/lubricant and the swarf precipitation, and that the finish machined work piece is very oily from the machining operation and is forwarded in this condition to the follow-up system.
Methods are also known by which the workpieces are brought into the working area through an opening closable by a loading door by means of a rapid robot or robot resembling device with dual grippers. The disadvantages of these solutions are the relatively large amount of apparatus required, the sensitivity to vibration, and the relative inaccuracy of work piece positioning due to the loading system being mostly located way outside the machine, and here again the discharge of oily dripping workpieces.
Machines with a rapid work piece changer are used to advantage in mass production, such as in automobile gear box manufacture, where the machine must seldom be setted up for a different work piece, and the cost of the automation can be amortized within a short time. In medium and small series production however, where the machine is setted up relatively frequently, automatic work piece loading is often not economic due to set up costs. Here a standard machine without automatic work piece loading is often given preference.
From the point of view of the machine manufacturer, therefore, the optimum economic solution is a high performance standard machine which can be supplied with or without a work piece loading device. In the case of the known solutions with rapid integrated loading system, the constructional deviations from the relevant standard machine with manual loading are so great however, that the high demands on a high performance automation cannot be fulfilled by the simple supplementation of the standard machine with a work piece loader.